Lattice strain accommodation and absence of pre-transition phases in Ni sub(50) Mn sub(25+x) In sub(25-x)

Abstract

The stoichiometric Ni sub(50) Mn sub(25) In sub(25) Heusler alloy transforms from a stable ferromagnetic austenitic ground state to an incommensurate modulated martensitic ground state with a progressive replacement of In with Mn without any pre-transition phases. The absence of pre-transition phases like strain glass in Ni sub(50) Mn sub(25+x) In sub(25-x) alloys is explained to be the ability of the ferromagnetic cubic structure to accommodate the lattice strain caused by atomic size differences of In and Mn atoms. Beyond the critical value of x = 8.75, the alloys undergo martensitic transformation despite the formation of ferromagnetic and antiferromagnetic clusters and the appearance of a super spin glass state.